New to ISPConfig, would like some information

I've just started my first 'real' job today and it involves ISPConfig. I've just finished school last year and don't have much Linux experience.

My new boss gave me a server, a Debian CD and the link to this page. He told to read up and learn about ISPConfig a bit before he unleashes me on his live system. He is out of town for the week on business and I'd like to take this opportunity to do some self study before he comes back next week and my official training starts.

So far I've managed to get the server up and running to the stage where I get to the login screen, thanks to the great tuts on this site. This server is not live, it is just running on our LAN, but I think I would set up a live server at home tonight and muck around with it a bit

I would like to ask a few questions and would really appreciate some help from the community.

1) Can I use dyndns to setup my server at home, if not I'll ask one of my colleagues to give me a public IP
2) What ports need to be forwarded from my router. Currently I can only pick up port 80, but would imagine port 25 and 110 also needs to be opened for mail access
3) When I create a website for a client,
a) do I create a FTP user for this client to access my server?
b) where does the website files go?

For now, I think this will get me going. Thanks in advance to everyone who is willing to help

1) Can I use dyndns to setup my server at home, if not I'll ask one of my colleagues to give me a public IP yes as long as dyndns points to your public ip at home

2) What ports need to be forwarded from my router. Currently I can only pick up port 80, but would imagine port 25 and 110 also needs to be opened for mail accessPorts 80 (HTTP), 8080 (ISPConfig Admin Access), 21 (FTP), 25 (SMTP), 110 (POP3) & 443 (SSL (optional))
3) When I create a website for a client,
a) do I create a FTP user for this client to access my server?yes, under Sites>FTP-User
b) where does the website files go?When logged into the FTP, files go into the /web/folder

Another question please. I have set up a server at home and created the following DNS records as well as registered a domain. I have set up this domain as a new client and created a mailbox for myself, yet when I send a test mail from another mail account, I get a msg stating "550 Invalid recipient domain"